1. Field of the Invention
The invention relates to a secondary battery having an electrode body as a generating element which is accommodated in a pack, from which electric power as generated by the electrode body is taken out through a pair of positive and negative electrode terminals, such as lithium ion secondary batteries and lithium polymer secondary batteries.
2. Description of the Related Art
In recent years, the demand for portable electronic appliances including information appliances such as notebook personal computers, mobile communication instruments such as mobile telephones, and video cameras is increasing rapidly. Sealed small-sized secondary batteries such as nickel-cadmium batteries, nickel hydrogen batteries, and lithium ion batteries are frequently used as a power source of such an electronic appliance. Above all, lithium ion secondary batteries are employed in various fields while making the most of characteristics such as high voltage, high energy density and lightweight.
In particular, as a countermeasure to the liquid leakage which is problematic in the case of using a liquid based electrolytic solution, for example, there is proposed a so-called polymer lithium ion secondary battery using, as an electrolyte, a gel-like polymer film having a polymer impregnated with a non-aqueous electrolytic solution or by using an electrolyte in a fully solid state.
Such a polymer lithium ion secondary battery is being further developed for the purpose of meeting the demands for respective electronic appliances in recent years, such as downsizing, lightweight and slimming, while making the most of a characteristic that a degree of freedom of the battery shape is high in addition to the characteristics of a battery such as high energy density and lightweight.
Usually, in such a battery, for example, as illustrated in FIG. 37, a single cell 301 made of a laminate of battery elements is accommodated together with a connecting substrate 302 provided with a protective circuit and terminals in a pair of upper and lower plastic cases 303, 304, thereby forming a battery pack 300 (see, for example, Patent Document 1). Joining of the plastic cases 303, 304 having the single cell 301 accommodated therein is usually carried out by ultrasonic welding.
Here, in order to ensure mechanical strengths against falling, vibration or the like, the battery pack 300, an exterior of which is configured by the plastic cases 303, 304, is required to be formed so as to have a considerable thickness, and therefore, it was difficult to devise to achieve downsizing or slimming of the battery pack 300 itself.
Patent Document 1: JP-A-2002-8606